A large volume translation project is always welcome from a revenue perspective. However, it has a few inherent challenges that must be addressed and resolved before getting into the translation phase.
It is essential that the agency is realistic about the time lines regarding the submission of documents. In setting or agreeing to a deadline there are a number of factors which need to be taken into consideration.

The type of document: Is it a technical manual, which will require a specific vocabulary or something more generic?

Language nuances: Does it need a specific dialect to be used?

Human resources available: What size of team can be devoted to the project? Are all the translators available for the entire duration of the project? Will you be able to arrange substitutes if required?

Method of delivery: Do the documents need to be handed over in physical copy or can they be emailed? This will affect the overall time required from receipt of the original document to delivery of the final translated one.

Specific software requirements: Are there diagrams or other specific elements which may require the use of specialized software?

The project manager then needs to work out an estimate of the number of words that need to be translated per day to make the deadline. Take stock of the translators available and check if their speed of translating matches the required rate and whether their skill set suits the type of documents to be translated. Someone familiar with a subject will be far quicker at translating than someone who has never translated a similar topic earlier. Work with a team of 5 – 6 dedicated translators and have at least one or two additional resources that can be called upon in case of an emergency.
Before beginning, check with the client on terms that need to be maintained as in the original or select terms that need to be uniform across all documents. Draw up a list and circulate this to the translators.
If it is a large manual with multiple chapters, set deadlines for the delivery of each chapter. Discuss with the client that it would be more convenient to send a few chapters at a time rather than the entire manual at one shot. This also allows the client to go through the initial chapters and ensure that the tonality and language are in tune with their requirements. Should there be any changes required they can be implemented in all documents going forward.
Assign similar chapters/ themes to the same people, as they translate their familiarity with the subject and therefore speed of translation will improve.
It is important that the documents are scrutinized as they are sent in by the translators, before they are shared with the client. Ensure that there is constant communication with the translator team so that everyone is on the same page and aligned with regard to the target.
Set weekly targets, and track these very closely to ensure that the project proceeds as per the timeline. Should there be any unavoidable circumstance which is likely to delay the project, inform the client immediately.
Communication is the key to ensuring success in a large project. Communication with the client as well as within the group translating the documents will prevent a scenario where there is a discrepancy in expectation vs. delivery. What do you think? How was your experience while managing a big translation project?